Traditionally, when refrigerant charged refrigeration systems were repaired, the refrigerant charge was simply loosed to the atmosphere as necessary to accomplish the repairs. In recent times, it has become increasingly desirable to capture and reuse the refrigerant charges for a number of reasons; refrigerant pollution of the atmosphere is perceived as environmentally destructive, government regulations now limit the release of fluorocarbon refrigerants to the atmosphere, and the cost of refrigerant materials has increased making the disposal and replacement of the refrigerant charge increasingly costly.
Refrigerant recovery devices of the prior art have drawn refrigerant from the fluid circuits of charged refrigeration systems, compressed and cooled the refrigerant to a liquid state, and, in some cases purified the refrigerant, for storage and reintroduction to the same refrigeration system after repair has been accomplished or for use in other refrigeration systems. Increasingly stringent government regulation limiting the release of refrigerants to the atmosphere require that recovery systems pull increasingly deep vacuums on the refrigeration fluid circuit to satisfactorily complete the recovery process. To achieve such vacuums, recovery apparatus of the prior art have utilized two pumps, generally a centrifugal compressor, which is utilized until a vacuum begins to form in the refrigeration system fluid circuit, and a positive displacement vacuum pump, which draws refrigerant fluid from the circuit after a predetermined negative gauge pressure is achieved.
The positive displacement pumps of the prior art devices must operate at high compression ratios to draw a sufficiently deep vacuum on a refrigeration which increases wear and the incidence of damage to pump motors and valves. The presence of two pumps increases the cost, mechanical complexity and weight of these recovery systems of the prior art. Further, maintenance costs of these systems are high because two different types of pumps must be maintained and, thus, parts must be inventoried and service persons trained for each.